CHARACTERISTICS OF THE KYOTO-UNIVERSITY LEAD SLOWING-DOWN SPECTROMETER (KULS) COUPLED TO AN ELECTRON LINAC

A lead slowing-down spectrometer coupled to a 46 MeV electron linear a ccelerator (linac) was installed at Research Reactor Institute, Kyoto University (KURRI). The size of this Kyoto University Lead Slowing-dow n Spectrometer (KULS) is 1.5 x 1.5 x 1.5 m(3), and it is covered with Cd sheets 0.5 mm thick. One of the eleven experimental holes in the KU LS is covered with 10 to 15 cm thick bismuth layers to suppress high e nergy capture gamma-rays from lead. The characteristics of this KULS h ave been experimentally obtained and the results are compared with the predicted values by Monte Carlo calculations using the MCNP code. 1) The slowing-down constant K in the relation E = Klt(2) between the neu tron slowing-down time t and energy E is 190 +/- 2 (keV mu s(2)) for t he bismuth hole and 156 +/- 2 (keV mu s(2)) for an ordinary lead hole, respectively. The K values agree with the calculated ones. 2) The mea sured energy resolution Delta E/E at full-width-at-half-maximum (FWHM) was about 40% for both holes, while the calculated values were lower by about 10% than the measured ones in the relevant energy region. 3) The neutron energy spectrum from 0.01 eV to 20 MeV and the spatial dis tribution of neutrons in the KULS were measured by the foil activation method. The angular neutron spectrum perpendicular to the linac elect ron beam was also obtained experimentally in the energy range from a f ew eV to about 10 MeV by the neutron time-of-flight (TOF) method. The measured results are compared with the calculated ones in which we hav e used the three evaluated nuclear data JENDL-3, ENDL-85 and ENDF/B-IV for lead. Through the comparison a check on the nuclear data has been performed.